Returning to public ownership will cost nothing?

According to John McDonell returning services back to public ownership will cost the public nothing.Mr McDonell said money could be borrowed to buy these services, then the money would be repaid when a profit is made. But who would the money be borrowed from?

And those services would be put into the hands of the workforce? Is this a good idea. Is this Corbyn wanting to turn the UK into a socialist type country?